Police have announced that the teenager fired three shots at the officer, who was off-duty and working as private security at the time of the incident.
Crowds blocked a major street in the largely African-American neighborhood of Shaw as demonstrators chanted anti-law enforcement slogans and attacked their vehicles.
Missouri shooting: Armed or not?
The officer confronted three black teens, one of whom allegedly fired three shots from a 9mm Ruger handgun, which was later recovered from the scene along with three projectiles.
The officer, who was in uniform at the time, fired at least 17 rounds in response, killing the suspect and escaping injury himself.
“An investigation will decide if the officer’s behavior was appropriate,” said police chief Dotson.
The victim has been identified by relatives as Vonderrit Myers Jr., 18. His mother, Syreeta Myers, told the Associated Press during a phone call that her son wasn’t armed, and was holding a sandwich at the time.
Missouri shooting: Further protests planned
The shooting comes before planned protests against the shooting of unarmed African-American teenager Michael Brown in Ferguson, just 16 miles down the road from Shaw.
At the initial demonstrations in Shaw, protesters did not attack or damage businesses as they did in Ferguson. The police approach was altogether different too, with no attempt to remove protesters from the street or use riot gear.
It has been reported that some social media postings called for the support of residents of Ferguson at the protests in Shaw. Increasing cooperation between protests groups will also be on show at the planned “Weekend of Resistance” this week.
Protest marches, acts of civil disobedience and a mass meeting at the Chaifetz Arena at Saint Louis University have all been scheduled by organizers.
They predict that thousands of people will participate to voice their anger. The event has the support of major labor organizations such as the A.F.L.-C.I.O..
The shooting of Vonderrit Myers Jr. will only add fuel to the flames at an already sensitive time in the area.